Objective: Informal caregivers (ICs) are relatives, friends, and partners who have a significant relationship with and provide assistance (i.e., physical, emotional) to a patient with a life- threatening, incurable illness. The multidimensional burden that results from providing care to a patient with cancer is well documented, and as a result, a growing number of psychosocial interventions have been developed specifically to address this burden. The purpose of the present study was to characterize the state of the science of psychosocial interventions for informal cancer caregivers. Method: A comprehensive systematic review of interventions for cancer caregivers was conducted via an electronic literature search of publications between 1980 and January 13, 2011. A final sample of 49 interventions was reviewed in detail. Results: The interventions, which varied in terms of modality and patient population, fell into the following eight categories: psychoeducation, problem-solving/skills building interventions, supportive therapy, family/couples therapy, cognitive-behavioral therapy, interpersonal therapy, complementary and alternative medicine interventions, and existential therapy. Benefits and disadvantages of each of the categories are discussed, with special attention given to studies that produced null findings. Significance of results: Beyond specific techniques, structured, goal-oriented, and time-limited interventions that are integrative appear to be the most feasible and offer the greatest benefits for ICs of cancer patients. Future studies are needed to examine the specific benefits and challenges of delivering interventions in alternative modalities (Internet, Skype) so that the needs of a greater number of ICs may be addressed.